The present invention relates in general to control of reflective-type sensors in reproduction apparatus, and more particularly to an automatic control system for reflective-type sensors.
In typical commercial electrostatographic reproduction apparatus (such as copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photo-conductive member having dielectric characteristics (hereinafter referred to as the dielectric member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric member. A receiver sheet is then brought into contact with the dielectric member, and an electric field applied to transfer the marking particle developed image to the receiver sheet from the dielectric member. After transfer, the receiver sheet bearing the transferred image is transported away from the dielectric member, and the image is fixed (fused) to the receiver sheet by heat and pressure to form a permanent reproduction thereon.
Such reproduction apparatus utilize receiver sheet sensors to determine sheet width, length, or position of a sheet along a sheet transport path. Additionally, receiver sheet sensors may be used at various locations along the sheet transport paths to determine sheet jam conditions. One commonly used type of sheet sensor comprises a light emitter/light detector pair. Generally the light emitter is an LED (light emitting diode) used as a transmitter of radiant energy, and a photocell, photodiode or phototransistor which receives the radiant energy and produces a signal indicative thereof. The sheet sensor can be either reflective or transmissive. That is, with the reflective type sensor, a sheet moves past an emitter and reflects light to an adjacent detector; while with the transmissive type sensor, a sheet moves between the emitter and detector and blocks the radiant energy from the emitter. Reflective type sensors are preferred because of their ability to detect transparent sheet material (i.e., transparencies).
It is important that the sheet sensors function properly in order to assure that information is reproduced on receiver sheets in a manner which provides user acceptable copies. Moreover, misfeeds and/or multifeeds of receiver sheets must be reliably detected in order to prevent major malfunctions of the reproduction apparatus. While sheet sensors of the above described type are relatively simple and easy to employ in typical reproduction apparatus, they are susceptible to control intricacies due to the fact that each sensor may be "seeing" a different background. That is, the background material that each sensor is looking at may be of a different reflectivity, and the distance to such background material may be different.